Lighting device

Abstract

Disclosed is a lighting device including a light guide plate, a plurality of LEDs, a prism sheet disposed on a side toward the upper surface of the light guide plate, and a reflective sheet disposed on a side toward the lower surface of the light guide plate. The plurality of LEDs are arrayed on a side surface corresponding to a first side of the light guide plate in a first direction along the first side. The prism sheet includes a first prism array that is formed on a surface facing the light guide plate. The first prism array includes prisms that are extended in the first direction and arrayed in a second direction perpendicular to the first direction. The upper surface of the light guide plate and the prism sheet sandwich a diffusion sheet therebetween. The diffusion sheet has a haze value between 30% and 65% when measured in compliance with JIS K7361. The prisms on the first prism array have an apex angle between 55 degrees and 66 degrees.

What is claimed is: 
     
       1. A lighting device comprising:
 a light guide plate; 
 a plurality of light emitting diodes; 
 a prism sheet that is disposed on a side toward an upper surface of the light guide plate; and 
 a reflective sheet that is disposed on a side toward a lower surface of the light guide plate, wherein 
 the plurality of light emitting diodes are arrayed on a side surface corresponding to a first side of the light guide plate in a first direction along the first side, 
 the prism sheet includes a first prism array that is formed on a surface facing the light guide plate, 
 the first prism array includes prisms that are extended in the first direction and arrayed in a second direction perpendicular to the first direction, 
 the upper surface of the light guide plate and the prism sheet sandwich a diffusion sheet therebetween, 
 the diffusion sheet has a haze value between 30% and 65% when measured in compliance with JIS K7361, 
 the prisms on the first prism array have an apex angle between 55 degrees and 66 degrees, 
 a second prism array that is formed on the upper surface of the light guide plate, extended in the second direction, and arrayed in the first direction; and 
 a third prism array that is formed on the lower surface of the light guide plate, extended in the first direction, and arrayed in the second direction, wherein 
 a pitch of the prisms formed on the first prism array is greater than a pitch of prisms formed on the second prism array and a pitch of prisms formed on the third prism array. 
 
     
     
       2. The lighting device according to  claim 1 , wherein
 the haze value of the diffusion sheet is between 30% and 55% when measured in compliance with JIS K7361, and 
 the apex angle of the prisms on the first prism array is between 59 degrees and 66 degrees. 
 
     
     
       3. The lighting device according to  claim 1 , wherein
 the haze value of the diffusion sheet is between 35% and 55% when measured in compliance with JIS K7361, and 
 the apex angle of the prisms on the first prism array is between 60 degrees and 64 degrees. 
 
     
     
       4. The lighting device according to  claim 1 , wherein
 a direction of a chief ray of light emitted from the upper surface of the light guide plate is tilted with respect to a normal of the upper surface of the light guide plate. 
 
     
     
       5. The lighting device according to  claim 4 , wherein
 an angle between a direction of a chief ray of light emitted from the prism sheet and a normal direction of the prism sheet is smaller than the angle between the direction of the chief ray of light emitted from the upper surface of the light guide plate and the normal of the upper surface of the light guide plate. 
 
     
     
       6. The lighting device according to  claim 4 , wherein
 a direction of a chief ray of light emitted from the prism sheet is a same as a normal direction of the prism sheet. 
 
     
     
       7. A lighting device comprising:
 a light guide plate; 
 a plurality of light emitting diodes; 
 a prism sheet that is disposed on a side toward an upper surface of the light guide plate; and 
 a reflective sheet that is disposed on a side toward a lower surface of the light guide plate, wherein 
 the plurality of light emitting diodes are arrayed on a side surface corresponding to a first side of the light guide plate in a first direction along the first side, 
 the prism sheet includes a first prism array that is formed on a surface facing the light guide plate, 
 the first prism array includes prisms that are extended in the first direction and arrayed in a second direction perpendicular to the first direction, 
 the upper surface of the light guide plate and the prism sheet sandwich a diffusion sheet therebetween, 
 the diffusion sheet has a haze value between 30% and 65% when measured in compliance with JIS K7361, 
 the prisms on the first prism array have an apex angle between 55 degrees and 66 degrees, 
 a second prism array is formed on the upper surface of the light guide plate, the second prism array is extended in the second direction, and arrayed in the first direction, 
 a third prism array is formed on the lower surface of the light guide plate, the third prism array is extended in the first direction, and arrayed in the second direction, and 
 the apex angle of the prisms formed on the first prism array is smaller than an apex angle of prisms formed on the second prism array and an apex angle of prisms formed on the third prism array. 
 
     
     
       8. The lighting device according to  claim 7 , wherein
 a direction of a chief ray of light emitted from the upper surface of the light guide plate is tilted with respect to a normal of the upper surface of the light guide plate. 
 
     
     
       9. The lighting device according to  claim 7 , wherein
 an angle between a direction of a chief ray of light emitted from the prism sheet and a normal direction of the prism sheet is smaller than the angle between the direction of the chief ray of light emitted from the upper surface of the light guide plate and the normal of the upper surface of the light guide plate. 
 
     
     
       10. The lighting device according to  claim 7 , wherein
 a direction of a chief ray of light emitted from the prism sheet is a same as a normal direction of the prism sheet. 
 
     
     
       11. A lighting device comprising
 a light guide plate; 
 a plurality of light emitting diodes; 
 a prism sheet that is disposed on a side toward an upper surface of the light guide plate; and 
 a reflective sheet that is disposed on a side toward a lower surface of the light guide plate, wherein 
 the plurality of light emitting diodes are arrayed on a side surface corresponding to a first side of the light guide plate in a first direction along the first side, 
 the prism sheet includes a first prism array that is formed on a surface facing the light guide plate, 
 the first prism array includes prisms that are extended in the first direction and arrayed in a second direction perpendicular to the first direction, 
 the upper surface of the light guide plate and the prism sheet sandwich a diffusion sheet therebetween, 
 the diffusion sheet has a haze value between 30% and 65% when measured in compliance with JIS K7361, 
 the prisms on the first prism array have an apex angle between 55 degrees and 66 degrees, 
 a second prism array is formed on the upper surface of the light guide plate, the second prism array is extended in the second direction, and arrayed in the first direction; and 
 a third prism array is formed on the lower surface of the light guide plate, the third prism array is extended in the first direction, and arrayed in the second direction, and 
 a height of the prisms formed on the first prism array is greater than a height of prisms formed on the second prism array and a height of prisms formed on the third prism array. 
 
     
     
       12. The lighting device according to  claim 11 , wherein
 a direction of a chief ray of light emitted from the upper surface of the light guide plate is tilted with respect to a normal of the upper surface of the light guide plate. 
 
     
     
       13. The lighting device according to  claim 11 , wherein
 an angle between a direction of a chief ray of light emitted from the prism sheet and a normal direction of the prism sheet is smaller than the angle between the direction of the chief ray of light emitted from the upper surface of the light guide plate and the normal of the upper surface of the light guide plate. 
 
     
     
       14. The lighting device according to  claim 11 , wherein
 a direction of a chief ray of light emitted from the prism sheet is a same as a normal direction of the prism sheet.